The relationship between light evoked neuronal activity and glial cell responses in the vertebrate retina will be explored by a number of pharmacological and electrophysiological techniques. Ion specific microelectrodes will be used to study extracellular changes in potassium and intracellular levels of chloride and sodium. Intracellular studies will be directed towards the neuronal elements of the retina with the aim to determine the ionic basis of neuronal-neuronal interaction. An understanding of neuronal mechanisms is essential for interpretation of glial-neuronal relationships. Since K ion mediated glial responses contribute to the electroretinogram, it should be possible to reveal the specific neurons whose light evoked activity leads to changes in external K ion. In addition pharmacological agents which selectively interrupt specific neuronal pathways will be tested for their effects on different components of the ERG. The combination of these two approaches should lead to a more definitive understanding of the origin and neuronal basis of Muller cell generated components of the ERG. BIBLIOGRAPHIC REFERENCES: Dacheux, Ramon, and R.F. Miller. Photoreceptor-bipolar cell transmission in the perfused retina eyecup of the Mudpuppy. Science, 191, 963-964, 1976.